The present invention relates generally to a zooming lens system, and more particularly to a zooming lens system designed to cover a wide-angle zone and have a zooming ratio of approximately 3 or higher.
Recently available cameras have more sophisticated functions and, with this, a zooming lens system such as one used for a still camera is desired to be large in terms of zooming ratio and compact, so that the range from the wide-angle end of a larger field angle to the telephoto end having a long focal length can be covered by use of a single lens system.
Among wide-angle zooming lens systems so far proposed in the art, there is a two-unit type of zooming lens system comprising a negative lens unit and a positive lens unit, as viewed in order from the object side, with the separation between both the units being varied for zooming. Although this type of zooming lens system is beneficial for increasing the field angle at the wide-angle end, however, much difficulty is involved in making satisfactory correction of aberrations, because the pencil of rays is diverged by the negative lens unit on the object side and so the heights of the rays incident on the positive lens unit are increased. Generally, the zooming ratio achieved is at most approximately 2.
Among recently developed wide-angle zooming lens systems having a zooming ratio of approximately 3 or higher, on the other hand, there are four- or five-unit systems with the foremost lens unit being of the positive type. For instance, a lens system which comprises, in order from the object side, a first positive lens unit, a second negative lens unit, a third positive lens unit, a fourth positive lens unit and a fifth positive lens unit is proposed, as typically disclosed in JP-A 57(1982)-195213, JP-A 60(1985)-170817, JP-A 61(1986)-258220, and JP-A 62(1987)-186216. However, this and other known zooming lens systems have a particularly long full length at the wide-angle end and less than satisfactory in terms of compactness as well.